The present invention relates to a high-friction fluid seal used for high-friction sealing which includes a fluid seal lip provided on the working fluid filling side to intercept a working fluid and a dust lip provided on the working fluid non-filling side (the outer side) of the fluid seal lip to intercept dust coming from the outside.
Also, the present invention relates to a cylinder-type shock absorber using a working fluid, which uses the aforementioned high-friction fluid seal as a seal between a piston rod and a cylinder body.
Shock absorbers, which are usually of a cylinder type, play a role in buffering external force by regulating the flow rate of a working fluid moving in the shock absorber, and are used for a suspension of a vehicle, an opening and closing part of a rear door of a vehicle, and the like.
The shock absorber described in Japanese Unexamined Patent Application Publication No. 2006-17161, which is one of the type of shock absorbers described above, is used for a vehicular suspension. In the sealing structure of the shock absorber, deformation preventing means (9b, 9c) (here, reference characters used in Japanese Unexamined Patent Application Publication No. 2006-17161 are shown in parentheses) are provided on an inclined face (9a) for lip storage of a rod guide (5) on the cylinder side with which the inner surface of an outer peripheral lip (18) of an oil seal (6) is in contact, by which seal failure caused by assembling work can be prevented.
The oil seal (6) used in this shock absorber has the same basic configuration as that of the high-friction fluid seal in accordance with the present invention. The oil seal (6) includes an oil lip (15) for intercepting working fluid (“working oil” in Japanese Unexamined Patent Application Publication No. 2006-17161), which is provided on the working fluid filling side, and a dust lip (14) for sealing dust coming from the outside, which is provided on the working fluid non-filling side (the outer side) of the oil seal (15).
Usually, a shock absorber used for a suspension is provided so that the tip end of the rod (4) is on the upside, and is configured so that the dust lip (14) thereof prevents dust (including rainwater and sometimes oil, etc. mixed in a puddle) coming from the outside from entering therein.
The dust lip (14) configured as described above cannot prevent oil film formed on the extension stroke of the oil lip (15), which comes inversely from the inside, from leaking out.
On the other hand, the shock absorber used for a suspension has a problem in that it is difficult to obtain a damping force at very low speeds and very small vibrations by the buffering action of working fluid. Therefore, in recent years, a high-friction fluid seal for high-friction sealing has been proposed which can obtain a damping force at very low speeds and very small vibrations by a frictional force between the fluid lip of fluid seal and a piston rod.
In this case, as a method for high-friction sealing, there are a method in which the friction coefficients of the working fluid and the material of the fluid seal are increased and a method in which the tightening force of the fluid seal on the piston rod (surface pressure of contact surface between both of the elements) is increased.
However, in both methods, a working fluid film formed on the contact surface between the fluid lip of the high-friction fluid seal and the piston rod is pushed out in the state in which the shock absorber is not operated for a long period of time (for example, parking time), so that the working fluid film may break.
Also, in the fluid seal for high-friction sealing, a slide of the contact surface, that is, the sliding contact between the fluid lip and the piston rod is restrained to a high degree.
Therefore, for these reasons, if the shock absorber using the high-friction fluid seal is left in an inoperative state for a long period of time, the fluid lip and the piston rod stick together. If the shock absorber is operated (the vehicle or the like is operated) in this state, a gap (opening) is formed in a part of the circumference of the contact surface between the fluid lip and the piston rod, and therefore the working fluid may leak out.
The working fluid leaking out of the fluid lip remains once in a fluid reservoir, which is a space between the fluid lip and the dust lip. However, since the dust lip does not prevent the working fluid from leaking from the inside of the dust lip to the outside thereof as described above, the working fluid leaking out of the fluid lip passes through the dust lip and is gradually discharged to the outer side (the atmosphere side), this state being judged to be working fluid leakage (oil leakage).
The working fluid leakage of this type occurs only when the vehicle is moved suddenly after being left for a long period of time, and the amount of leaking working fluid is also small. Therefore, this leakage differs from progressive leakage such that a flaw is induced at the outer periphery of the piston rod, resulting in leakage. However, this leakage gives a sense of unease to the user of vehicle, so that improvement has been demanded.
FIGS. 7(a)-7(c) show a background art of the present invention, showing a gas spring using a seal capable of preventing this leakage of working fluid. FIG. 7(a) is a longitudinal sectional view of the gas spring, FIG. 7(b) is an enlarged sectional view of a part of a seal, and FIG. 7(c) is a partially enlarged sectional view of FIG. 7(b). This gas spring (shock absorber) is one described in Japanese unexamined Patent Application Publication No. 2002-286067.
This gas spring 50 includes a seal 40 having the above-described features, and also includes a cylinder body 41, a body-side connecting part 41a, a piston 42, a piston rod 43, a rod-side connecting part 43a, a bearing 44, and a retainer 45 as the basic components of a shock absorber.
The interior of the cylinder body 41 is divided into a gas chamber A and a fluid chamber L by the piston 42. The piston 42 is provided with a port 42a, by which high-pressure gas in the gas chamber A can flow between the gas chamber A and the fluid chamber L.
By the above-described configuration, the gas spring 50 always urges a rear door in the opening direction and gives a proper damping force to the opening/closing movement of the rear door by means of the pressure of the high-pressure gas in the gas chamber A in a posture shown in FIG. 7(a), that is, in the state in which the body-side connecting part 41a is connected to the upper side (the rear door side) and the rod-side connecting part 43a is connected to the lower side (the vehicle body side).
The seal 40, which is a feature of the gas spring 50, includes a sub lip 31, a main lip 32, an insert metal 33, and an outer peripheral lip 34 as shown in FIG. 7(b). A fluid reservoir S′, which is a space between the sub lip 31 and the main lip 32, is made a large space, as compared with the conventional gas spring, by providing the main lip 32 on the inside (the fluid chamber L side) of the insert metal 33 and the sub lip 31 on the outside thereof.
Also, as shown in FIG. 7(c), the lip tip end of the sub lip 31 is formed into a substantially trapezoidal shape. Specifically, the lip tip end of the sub lip 31 has an upper face a, a side face b, and a bottom face c, and an angle θ1 between the upper face a and the piston rod 43 is formed so as to be larger than an angle θ2 between the side face b and the piston rod 43. Thereby, the working fluid is prevented from leaking in such a manner that the lip tip end always scrapingly returns the working fluid in the fluid reservoir S′ in the direction toward the fluid reservoir S′ (paragraph [0030] of Japanese Unexamined Patent Application Publication No. 2002-286067).
By the above-described configuration, according to this gas spring 50, the working fluid can be prevented from leaking out of the sub lip 31. Also, in the case where the gas spring 50 is used in a posture such that the sub lip 31 is on the downside, a problem in that dust, water, and the like intrude from the outside is less liable to occur.
However, in the case where the gas spring 50 is used in a reverse posture as the shock absorber for vehicular suspension as described in Japanese Unexamined Patent Application Publication No. 2006-17161, that is, it is used in a posture such that the sub lip 31 is on the upside, the sub lip 31 cannot perform function as a dust lip, that is, cannot prevent dust and water coming from the upper outside from intruding. Therefore, the seal 40 of such a gas spring 50 cannot be used as a shock absorber for suspension. Japanese Unexamined Patent Application Publication No. 2006-17161 discloses a coarse face 9b serving as a deformation preventing means shown in FIGS. 1 and 3, and a protrusion 9c serving as a deformation preventing means shown in FIG. 4. Japanese Unexamined Patent Application Publication No. 2002-286067 discloses a seal 19 shown in FIGS. 1 to 3, and a sub lip 23 thereof.